The subject matter of the invention relates to a nozzle, and more particularly to a nozzle for dispensing liquids and other flowable materials hereinafter called fluids, in a highly controllable fashion through an apparatus that is mechanically simple, dimensionally accurate, operationally efficient and reliable in the form of jets or streams herein called fluid paths or droplets.
Dispensing controllably small quantities of fluid through a nozzle that electrostatically charges the fluid has been heretofore proposed. A typical apparatus might take the form of the corona charging arrangements found in DeVottorio's U.S. Pat. No. 4,341,347, or the induction charging nozzles disclosed in Law's U.S. Pat. No. 4,004,733. Inherent in the geometry of this art is a small dispensing orifice for the fluid, a some mechanical means like the spinning disk of Hopkinson's U.S. Pat. No. 4,215,818, or aerodynamic means as disclosed in Juvinall's U.S. Pat. No. 4,002,777 which finely divides the fluid continuum into droplets.
Problems develop in the aforementioned devices because of the small orifices. The orifices cause considerable difficulty in obtaining reliable function of the nozzle. They have a tendency to become clogged with foreign material, and also encounter high wear due to the abrasive nature of dispensed fluids forced at high local velocities through the orifice. In some processes, the mechanical or aerodynamic dropletization means can be detractive due to either its energy requirement or the creation of excess volume leading to oversprayed material. In all nozzle design application efficiency is important.
The requirement of providing electrical charges to the sprayed liquid creates further complications. A process would ideally provide a high percentage of the theoretical electrostatic charge limit, referred to as the Rayleigh Charge, on what typically may be a wide range of droplet or flow path sizes. This usually involves either conductive liquids or medium resistive liquids, but desirably would include all fluids. The charge has to be applied in a reliable manner taking into consideration aspects of personal safety. Hazards include sparking or arcs in the presence of flammatory solvent-borne materials, including paint, as well as the potential for operator shock. Energy efficiency has also become an important factor.
Another consideration of fluid nozzles is the desire for variability in droplet size, which normally translates into orifice size, and uniformity of droplet size, and control. Difficulties arise in the mechanical fabrication of small orifices. Small holes with any significant bore depth are difficult to fabricate due to the fragility of suitable tools. Consequently, little is found in standard commercial nozzling with orifices smaller than 0.001 inch diameter.
An additional complication is inherent in the class of liquids known as non-Newtonian fluids. With these fluids there is difficulty in obtaining proper acceleration characteristics as the fluid traverses a typical nozzle geometry. This class of fluids, found frequently in the adhesive field, possess viscosity properties that are affected by their local speed, creating loss of fluid uniformity and difficulty in pumping the fluid at conventional pressures. As a consequence, higher pressure of several orders is often necessary to dispense non-Newtonian fluids from typical nozzles.
It is therefore highly desirable to provide an improved electric fluid nozzle.
It is therefore highly desirable to provide an improved fluid nozzle and method which facilitates the dispensing of controlled amounts of fluid in a plurality of fine flow paths or droplets.
It is also highly desirable to provide an improved fluid nozzle and method which allows for a variation of flow.
It is also highly desirable to provide an improved fluid nozzle and method which avoids the problems characteristic of mechanical orifice devices.
It is also highly desirable to provide an improved fluid nozzle which is mechanically simple and inexpensive to manufacture.
It is also highly desirable to provide an improved fluid nozzle and method which is operationally efficient and cost effective.
It is also highly desirable to provide an improved fluid nozzle which is relatively free from frequent clogging caused by foreign material, and suitable for use over a wide range of fluid flow rates.
It is also highly desirable to provide an improved fluid nozzle having electrostatic characteristics such that a high percentage of the theoretical charge limit can be imposed upon the fluid.
It is also highly desirable to provide an improved fluid nozzle and method which provides a preselectable range of droplet sizes to be dispensed over a preselected number of dimensionally stable flow paths.
It is also highly desirable to provide an improved fluid nozzle and method having flow considerations and lends itself to dispensing of both high viscosity and low viscosity fluids, both non-Newtonian and Newtonian materials except for highly conductive and highly resistive fluids.
It is also highly desirable to provide an improved fluid nozzle for dispensing fluid in a highly controllable manner throughout its entire operational range.
It is also highly desirable to provide an improved fluid nozzle having exceptional reliability.
Finally, it is highly desirable to provide an improved fluid nozzle and method having all of the above-mentioned characteristics.